<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="box">盒子</div>
    <div class="box">盒子</div>
    <div id="nav">
        <ul>
            <li>首页</li>
            <li>产品</li>
        </ul>
    </div>
    <script>
     var boxs = document.getElementsByClassName('box');
     console.log(boxs);
     //2.querySelector 返回指定选择器的第一个元素对象  切记 里边的选择器需要加符号 .box #nav
     var firstBox = document.querySelector('.box');
     console.log(firstBox);
     var nav = document.querySelector('#nav');
     console.log(nav);
     var li = document.querySelector('li');
     console.log(li);
     //3.qureySeletorAll()返回指定的选择器的所有元素对象集合
     var allBox = document.querySelectorAll('.box');
     console.log(allBox)
     var lis = document.querySelectorAll('li');
     console.log(lis)
    </script>
</body>
</html>